Deformable optical mirror assemblies, including a face plate, are utilized in a variety of optical applications. These assemblies may be applied to both transmit and receive optical signals. In transmitting applications, after a correlated optical signal is produced by a laser or other photonic radiation emitting device, the correlated optical signal is reflected off the face plate of the optical mirror assembly. The face plate is controllably contoured such that the path of each component of the correlated optical signal (photon) is travelling in nearly the same direction as the others. Since virtually every photon of the optical signal is being transmitted parallel to each other, the photonic radiation can be transmitted over a very long distance (even up to many miles) with only minor reduction in the energy of the photonic radiation. These correlated optical signals can be utilized in transmitting information, as well as other applications.
In many applications where the mirror assemblies are located at the receiving end of the optical signals and the signals are being transmitted over relatively long distances, the waveforms of the correlated optical signal are corrected for transmission abnormalities by altering the shape of the face plate by using actuators. The shape of the waveforms is vital in controlling the content and/or energy of the transmitted signal. A very high percentage of all of the energy contained in the transmitted signal can be focused onto a relatively small area where a detector is located. Using deformable face plates, a weaker signal can be detected with the same precision as a stronger signal which is being reflected off the fixed face plate. This permits reliable signal transmission with less energy required to generate the signals.
One such optical mirror assembly is described in greater detail in the Detailed Description portion of this disclosure. This optical mirror assembly is relatively expensive to produce since many of the components are produced individually. The cost of such a complete, full sized, optical deformable mirror assembly can be over a million dollars. An expensive repair situation is presented when one or more actuators in the actuator array becomes disabled or malfunctions. There is no technique which permits replacement of the actuators with relative ease. When an actuator is found to be inactive in this embodiment that actuator is disabled. This results in not being able to adjust a small portion of the deformable face plate of the optical mirror assembly. As additional actuator assemblies become non-functional within a single system, the adjustability of the mirror as well as the benefits associated with having an adjustable or controllable optical mirror assembly quickly diminishes.
The actuators used in deformable optical mirror assemblies are required to cycle at an extremely rapid rate (at the magnitude of one thousand Hertz) since the optical mirror assembly contour must be precisely adapted to adapt to optical waveforms which change on a regular basis with each optical wave cycle. Therefore, during normal operation of the optical mirror assembly, individualized actuators usually cycle at a rapid rate. When one or more actuator assemblies are disabled, the ability of the face plate to compensate for deformed waveforms is reduced.
Another disadvantage of the optical mirror assembly illustrated in FIG. 1 is that it is difficult to mount the actuator assemblies to the face plate in a precise kinematic manner as defined in the Detailed Description. The portion of the actuator which mounts to the face plate itself is typically a flat surface affixed to the face plate by adhesive such as epoxy. Also, it is very difficult to mount the actuators precisely parallel to each other. This creates some inaccuracy as to where each actuator is mounted to the face plate. Such inaccuracy in mounting position causes uncertainty in displacement of each actuator to provide desired face plate deformation. Additionally, when the actuators are not parallel to each other, the flat surfaces of the actuators are mounted to the face plate cannot be parallel to (flush with) the face plate. As the actuators cycle with respect to each other, those actuators with a flat surface which is not precisely flush with the face plate provide a lateral force to the face plate when actuated. When the actuators are not parallel to each other, the lateral forces do not match, resulting in high cycling stresses being applied to the face plate itself. These stresses may result in an undesirable deformation in the face plate. It is also likely that during the actuator mounting process a continual lateral force can be created between the actuator and the face plate. Such force will likely produce undesirable deformations in the face plate.
Prior art patents which illustrate prior art removable face plate actuators include U.S. Pat. No. 4,923,302, which issued May 8, 1990 to Ealey et al.; U.S. Pat. No. 4,940,318, which issued Jul. 10, 1990 to Ealey et al.; U.S. Pat. No. 5,037,184, which issued Aug. 6, 1991 to Ealey; U.S. Pat. No. 5,037,190, which issued Aug. 6, 1991 to Ealey et al. (all of these patents being incorporated by reference in their entireties). These patents utilize screw threads to adjustably mount the actuators with respect to the face plate. There are several inherent limitations to using screw threads in mounting actuators.
A first limitation is due to the difficulty in achieving precise axial positioning of the actuators. It is very difficult to control axial positioning of actuators using screw threads where rotation of the actuators cause uncertain axial deflection. Uncertainty results from the screw threads having inherent hysteresis which is difficult to account for. A second limitation with screw mounted actuators is that the location where the actuator mounts to the face plate is difficult to precisely control since the actuator mounting holes may be out of skew, or the threads on the actuators may be incorrectly aligned. Screw threads are overly constraining as to the lateral positioning of the actuator with respect to the face plate. A third problem with screw thread mounted actuators is that, after considering the above two problems in which the actuators are being positioned in same undesired location, there may also be undesirable forces created between the actuator and the face plate. Such forces create deformations in the face plate which have to be compensated for or the overall accuracy of the optical mirror assembly is compromised. As a result, screw thread mounted actuators of the Ealey and the Ealey et al. patents do not truly represent a kinematic mount between the actuators and the face plate.
The above undesirable aspects of the screw thread mounts for actuators can be somewhat overcome by providing a relatively loose screw mount. There are some negative results in providing loose screw mounts to the actuator, however. A loose screw mount permits some play in the front of the actuator with respect to the backing plate. This is because loose screw mounts provide only limited control of positioning where the actuator contacts the face plate. A complex and involved process is involved where a skilled technician that is inserting (either manually or using a tool) the actuator must precisely position the actuator with respect to the loose screw mount. Loose screw mounts of also permits unscrewing of the actuator from its mount during the high frequency operation of the mirror assembly. An additional undesirable effect of using loose actuator screw mounts is that they provide an undesirable low spring constant between the actuator and its screw mount in all three directions, and about all three axes. It is desirable to build in high spring constants to achieve high natural frequencies out of the range of intended operation.
From the above, it can be appreciated that it is desirable to provide some configuration of optical mirror assembly in which at least certain actuators may be readily replaced as they become defective. It is also desirable to provide some technique by which actuators may be affixed to the face plate of the mirror assembly to reduce the stresses and deformations applied to the face plate. Additionally, it is desirable to provide an actuator mount configuration by which the location at which the actuator contacts the face plate can be controlled.